iStockphoto/Thinkstock(SEOUL, South Korea) -- North Korean authorities on Wednesday banned South Korean workers from entering the Kaesong Industrial Zone, an inter-Korean project just above the border.

The move was widely expected as Pyongyang has slowly ratcheted up tensions with a series of threats in the past few months, putting the South Korean government on edge over the safety of more than 800 workers still inside North Korea.

"We should stop this from going into the worst-case scenario," South Korean Defense Minister Kim Kwan-Jin said at a meeting of ruling party lawmakers. "But in case of crisis, we consider all options, including military actions."

Alongside the launch of its long-range missiles in December and a third nuclear test in January, North Korean rhetorical threats have been non-stop in recent weeks.

Its leader, Kim Jong Un, has vowed to launch a pre-emptive nuclear strike on the United States and South Korea in protest of the latest U.N. sanctions -- targeting the luxury goods presumably used by Kim's family and Pyongyang's privileged officials -- and the annual U.S.-South Korean military drills.

Forty-six South Korean workers and 28 vehicles are expected to return to the south on Wednesday -- a smaller number than expected because the South Korean companies opted to keep workers there to keep business production afloat. A total of 822 South Koreans and seven foreign workers are expected to stay inside the Kaesong complex for now.

The inter-Korean industrial complex is an economic joint venture conceived in 1998 to utilize South Korean capital and North Korean labor in an effort to promote collaboration and peace. About 123 South Korean companies produce a variety of labor-intensive products such as shoes, clothing, electronic goods and chemical products.

Several hundred South Korean workers shuttle back and forth across the border every day, including vehicles to deliver raw materials, machinery, finished products and food for the laborers.

The project is an important source of revenue for cash-stricken North Korea. Generating $2 billion a year in trade, more than 50,000 North Korean workers make $92 million in wages, which many suspect trickles into the regime rather than the workers' families.

The South Korean government expressed "deep regret" to the entry ban and urged it to be lifted immediately.

"In order to promote investment in North Korea as North Korea itself hopes, it is necessary for North Korea to build trust not only with the South, but also with the international community," Kim Hyung-suk, spokesman for South Korea's Ministry of Unification, said.

In an official statement, the ministry pointed out that North Korea should be "more predictable" in doing business to attract investments from abroad and warned the ban will have "negative repercussions."